Inductance coil fitted with iron dust core



p 3, 1940. H. c. HEBARD 2,213,311

INDUCTANCE COIL FITTED WITH IRON DUST CORE Filed Oct. 5, 1938 INVENTOR. HUG CHARLES HEBARD ATTORNEY.

Patented Sept. 3, 1940 UNITED STATES PATENT OFFICE Hugh Charles Hebard, Greenford, England, as-

signor to Johnson Laboratories Incorporated,

Chicago, Ill.

Application October 5, 1938, Serial No. 233,465 In Great Britain October 6, 1937 2 Claims.

This invention relates to inductance coils fitted with dust cores, 1. e. cores composed of a mass of magnetic particles electrically insulated from one another and serving to increase the in- 5 ductance oi the coils at high frequencies. Such coils are used as radiofrequency tuning coils for wireless receivers and for other purposes.

In order to enable the inductance of such coils to be set accurately for the purpose of tuning 10 a number 01' circuits to the same frequency it is convenient to provide for adjustment of the core relatively to the coil, but when two coils are electromagnetically coupled together such adjustment of the core usually alters the coupling to fl an undesirable extent. Serious difficulty then arises by reason of the impossibility of altering the sell inductance of one coil without disturbing the coupling between the coils.

According to the present invention, in order to go overcome this difiliculty in a simple manner, the core is divided into two parts one of which is placed in a region where the flux linking with both coils is relatively strong whilst the other is placed in a region where the flux links mainly with one coil only so that by adjustment of the last mentioned part of the core the self inductance of the last mentioned coil can be varied with but slight effect upon the mutual inductance of the two coils.

According to another aspect of the invention, variation of the inductance of one coil is eiiected by means of a variable air gap located in a region where the flux linking with one coil is strong as compared with the flux linking with both coils.

v The invention also provides an improved device ior adjusting the core relatively to' the coil, comprising a fixed sleeve formed with a helical camsurface at each end, a rod or bar rotatable and axially slidable in the sleeve and two projections fixed to the rod or bar, each oi. the projections being located against one of the helical cam surfaces so that rotation of the rod or bar causes the same to be displaced axially either forwards or backwards according to the direction of rotation.

The invention will be more readily understood from the following particular description with reference to the accompanying drawing in which:

Figure 1 is a sectional view of an inductance device constructed according to one term of the invention, Y

Figure 2 is a similar .view showing a modified construction embodying the improved adjusting device hereinbeiore referred to, and

Figures 3 and 4 are detail views showing the construction of the sleeveiormed with the hellcal cam surfaces.

The inductance coil shown in Figures 1 and 2 of the drawing comprises a multi-layer solenoidal 5 coil divided into sections in such a manner as to reduce the self-capacity of the coil. The coil I is mounted on a former 2 and a coupling coil 3 is mounted adjacent the coil I as shown.

The device is fitted with a dust core in the 10 v form of a rod or bar divided into two parts 4 and 5. The part 5 extends from a point intermediate the ends of the coil I up to and through the coupling coil 3. The part 4 is axially adjustable from a maximum inductance position in which 15 it may be in contact with the part 5 to positions in which the self-inductance of the coil l is reduced by reason of the air gap formed between the two parts of the core. It will be obvious that considerable variation of the sell inductance of go the coil I can be obtained by varying this air gap. 0n the other hand, the mutual inductance between the two coils is due mainly to linkage between the coupling coil 3 and that part of the inductance coil I which lies between the coupling g5 coil and the air gap. Consequently, variations of the air gap have comparatively little effect upon the coupling.

The core part 4 consists of a hollow cylinder or tube of magnetic material mounted on a rod 30 or stud 6 by which the core 4 is adjusted and held in adjusted position. In the form 01 construction shown in Figure 1 of the drawing adjustment is eifected by means of a lever arm I flxedto the stud 6 and projecting through a helical cam slot 8 in the former 2. It will be seen that by rocking the lever I so as to rotate the stud 8, a longitudinal movement can be imparted to the core I owing to the action of the lever l in the slot 8.

Figure 2 of the drawing shows a modified construction in which the stud 6 towhich the adjustable core 4 is attached has an extension 9 mounted to slide in a sleeve or hollow plug ll fixed in one end 01' the coil iormer 2. The sleeve or plug it is formed at its ends with helical cam surfaces H and I! which co-operate with studs or projections l3 and it formed on the part 8. The projecting end of the part 9 is formed with a head I! constructed so that it can be rotated by means of a screw-driver or other suitable tool. 0

The stud S and its extension 9, together with the projections l3 and I4 and head I! may consist of a moulding made of vulcanized rubber, synthetic resin or other suitable plastic material and may be formed in one piece.

The sleeve or plug I is made of similar material and in order to enable it to be mounted on the part 9 it is constructed in two halves, each of which consists of one half turn of a helicoid. The two parts are held together by means of a ring I6 and they are formed with suitable interengaging projections or recesses I! as indicated in Figure 3 of the drawing so as to prevent relative displacement of the two halves at the two diammetrically opposed joints between them.

When the head I is rotated by means of a screw-driver or otherwise, the core part 4 is moved towards or away from the part 5 according to the direction of rotation of the head 15. When the desired adjustment has been made, a quantity of fusible plastic material which will adhere to the material of the head l5 and sleeve I0 may be applied to the head [5 in a molten condition in such a way as to unite the head l5 to the sleeve l0 and prevent relative rotation between them. By this means the device is sealed in adjusted position.

The coil shown in the drawing is intended to be used as a radio frequency coupling coil. The coil I is tuned by means of a condenser and the coil 3 forms part of an aperiodic anode or grid circuit which is coupled to the tuned circuit by virtue of the electromagnetic coupling between the coils l and 3.

Having thus described my invention, what I claim is:

1. In a high-frequency inductance device having an adjustable ferromagnetic core and including a coil, a device for adjusting the core relatively to the coil comprising a fixed sleeve formed with a helical cam surface at each end, a rod rotatable and axially slidable in said sleeve and'having two projections fixed thereto, each of said projections being located against one of said helical cam surfaces so that rotation of the rod causes the same to be moved axially relatively to the coil according to the direction of rotation, said sleeve being composed of two halves each of which has the general form of one-half turn of a helicoid for convenience in assembling said sleeve around said rod.

2. In a high frequency inductance device having an adjustable ferromagnetic core and a cooperating coil, the combination of a fixed sleeve aligned with said core and having similar end cam surfaces, a rod connected with said core and mounted in said sleeve for rptary and axial movements relatively to said sleeve, said rod having projections engaging said cam surfaces, whereby rotating said rod correspondingly moves said core axially of said coil, said sleeve'being sectional to facilitate assembly around said rod.

HUGH CHARLES HEBARD. 

